This application claims the priority benefit of Taiwan application serial no. 87106243, filed Apr. 23, 1998, the full disclosure of which is incorporated herein by reference.
1. Field of the Invention
This invention relates to radio transceivers, and more particularly, to a GFSK (Gaussian Frequency Shift Keying) radio transceiver for ISM (Industrial Scientific and Medical) wideband communication systems.
2. Description of Related Art
A radio transceiver is a communication device that allows the user to talk to another person at a remote side. It is widely used in portable communication devices, such as mobile phones of various standards as CT2, CT3, and various others. Radio transceivers of different standards are distinguished specifically by the particular frequency bands that they use for radio transmissions.
FIG. 1 is a schematic block diagram of a conventional radio transceiver which is specifically designed for radio communication in a particular frequency band, for example the ISM band of 902 MHz to 928 MHz (megahertz).
As shown, the conventional radio transceiver includes mainly a transmitter 10 and a receiver 12. In more detail, the transmitter 10 is composed of a power amplifier (PA) 14, a frequency synthesizer 16, and a Gaussian filter 18; and the receiver 12 is composed of a low-noise amplifier (LNA) 20, a mixer 22, an intermediate-frequency (IF) demodulator 24, and a frequency synthesizer 26. The frequency synthesizer 16 in the transmitter 10 is composed of a phase looked loop (PLL) circuit 28 and a pair of voltage-controlled oscillators (VCO) 30, 32; and the frequency synthesizer 26 in the receiver 12 is composed of a PLL circuit 34 and a VCO 36. Still further, the radio transceiver includes an antenna 42, a band-pass filter (BPF) 40, and a T/R (transmit/receive) switch 38.
The foregoing radio transceiver operates switchably in two modes: transmit mode and receive mode. In the transmit mode, the T/R switch 38 connects the antenna 42 and the BPF 40 to the transmitter 10. The data signal to be transmitted is first processed by the Gaussian filter 18. Then, the output of the Gaussian filter 18 is transferred to the frequency synthesizer 16 where the data signal is modulated by an RF (radio frequency) carrier signal generated by the VCO 30 in the frequency synthesizer 16. The modulated RF signal is then amplified by the PA 14. The amplified signal from the PA 14 is then transferred via the T/R switch 38 (which is now switched to the transmitter 10) and subsequently via the BPF 40 to the antenna 42 for transmission through the either to the receiving side.
In the receive mode, The other VCO 32 is used to generate a local oscillating signal LO1 for use in the receiver 12 to downconvert the received signal. The RF signal received by the antenna 42 first passes through the BPF 40 and subsequently through the T/R switch 38 (which is now switched to the receiver 12) to the receiver 12. In the receiver 12, the received RF signal is first amplified by the LNA 20. The amplified RF signal from the LNA 20 is then mixed by the mixer 22 with the first oscillating signal LO1 from the VCO 32 so as to downconvert it to a first intermediate-frequency (IF) signal. The first IF signal from the mixer 22 is further mixed by the IF demodulator 24 with the second local oscillating signal LO2 from the VCO 36 in the frequency synthesizer 26 so as to further downconvert the first IF signal to a second IF signal with an even lower frequency. After this, the original data form of the received signal can be extracted from the second IF signal through a quadrature detection means in the IF demodulator 24.
One drawback to the foregoing radio transceiver, however, is that it requires the use of two frequency synthesizers, i.e., 16 and 26, which makes both the design and the manufacture of the radio transceiver more complex to carry out. The manufacturing cost is therefore considerably high. A conventional solution to this problem is to combine the two frequency synthesizers into one single unit. However, this solution requires the use of a wideband VCO, a fast switching time, and a large frequency shift in data switching, which would make the radio transceiver very difficult to realize. Moreover, since the PA 14 is a one-stage amplifier with a fixed gain, it can cause interference to other nearby radio transceivers and high power consumption to the radio transceiver itself, leading to a poor signal quality in transmitting and reception and a reduced number of radio transceivers that can be used at the same time and the same site.
As a summary, the prior art has the following drawbacks.
(1) First, it requires the use of two frequency synthesizers to implement, which makes both the design and the manufacture of the radio transceiver more complex to carry out.
(2) Second, the scheme of combining two frequency synthesizers into one single unit requires the use of a wideband VCO, a fast switching time, and a large frequency shift in data switching, which would make the radio transceiver very difficult to realize.
(3) Third, the power amplifier used in the prior art is a one-stage amplifier with a fixed gain, which would cause interference to other nearby radio transceivers and high power consumption to the radio transceiver itself, leading to a poor signal quality in transmitting and reception and also a reduced number of radio transceivers that can be used at the same time and the same site.
It is therefore an objective of the present invention to provide a GFSK radio transceiver for ISM wideband communication, which can be used in conjunction with a time-division duplex (TDD) system and operate selectively in either half-duplex mode or full-duplex mode.
It is another objective of the present invention to provide a GFSK radio transceiver for ISM wideband communication, which utilizes a variable-gain power amplifier that can help improve the problems of interference and high power consumption that are drawbacks with the prior art.
It is still another objective of the present invention to provide a GFSK radio transceiver for ISM wideband communication, which utilizes only one single wideband VCO to generate an oscillating signal that can be used both as the carrier signal in the transmitter and as a local oscillating signal in the receiver, thus allowing the GFSK radio transceiver of the invention to be implemented with a fewer number of VCOs as compared to the prior art so that the manufacturing cost of the GFSK radio transceiver of the invention can be reduced.
In accordance with the foregoing and other objectives of the present invention, a new GFSK radio transceiver is provided for ISM wideband communication. The GFSK radio transceiver of the invention comprises a transmitter and a receiver.
The transmitter used for modulating transmitted signal into RF signal comprises a VCO and a variable-gain power amplifier. The VCO is used for generating an oscillating signal serving as a carrier signal for the transmitted signal. The variable-gain power amplifier, which is capable of being adjustable between a low-power gain and a high-power gain, is used for amplifying the RF signal.
The receiver, which is used for demodulating received signal into digital form, comprises a mixer, a local oscillator and an IF demodulator. The mixer is used for downconverting the received signal into a first IF signal by mixing the received signal with a first local oscillating signal which is fetched from the oscillating signal from the VCO in the transmitter. The local oscillator is used for generating a second local oscillating signal. The IF demodulator is used for downconverting the first IF signal from the mixer into a second IF signal by mixing the first IF signal with the second local oscillating signal.
Compared to the prior art, the GFSK radio transceiver of the invention can operate either in half-duplex mode or in full-duplex mode in a TDD system through micro-processor controls. Further, the GFSK radio transceiver of invention utilizes a variable-gain power amplifier that can improve the problems of interference and high power consumption that are drawbacks with the prior art. Moreover, the GFSK radio transceiver of the invention utilizes one single wideband VCO to generate an oscillating signal that can be used both as the carrier signal in the transmitter and as a first local oscillating signal in the receiver. This feature allows the GFSK radio transceiver of the invention to be implemented with a fewer number of VCOs as compared to the prior art, thus reducing the manufacturing cost.